Open AccessThe putative tumor suppressors EXT1 and EXT2 form a stable complex that accumulates in the Golgi apparatus and catalyzes the synthesis of heparan sulfate
Author(s) -
Craig McCormick,
Graeme Duncan,
K. Tina Goutsos,
Frank Tufaro
Publication year - 2000
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.97.2.668
Subject(s) - hereditary multiple exostoses , golgi apparatus , glycosyltransferase , biology , heparan sulfate , endoplasmic reticulum , gene , biochemistry , transmembrane protein , microbiology and biotechnology , glycosaminoglycan , receptor
Hereditary multiple exostoses, a dominantly inherited genetic disorder characterized by multiple cartilaginous tumors, is caused by mutations in members of theEXT gene family,EXT1 orEXT2 . The proteins encoded by these genes, EXT1 and EXT2, are endoplasmic reticulum-localized type II transmembrane glycoproteins that possess or are tightly associated with glycosyltransferase activities involved in the polymerization of heparan sulfate. Here, by testing a cell line with a specific defect in EXT1 inin vivo andin vitro assays, we show that EXT2 does not harbor significant glycosyltransferase activity in the absence of EXT1. Instead, it appears that EXT1 and EXT2 form a hetero-oligomeric complexin vivo that leads to the accumulation of both proteins in the Golgi apparatus. Remarkably, the Golgi-localized EXT1/EXT2 complex possesses substantially higher glycosyltransferase activity than EXT1 or EXT2 alone, which suggests that the complex represents the biologically relevant form of the enzyme(s). These findings provide a rationale to explain how inherited mutations in either of the twoEXT genes can cause loss of activity, resulting in hereditary multiple exostoses.